If you read this paragraph carefully, it clearly implies that spending "a great deal of time" using social media causes depression in some teens. Specifically, the "intensity of the online world" may "trigger" the problem.
The other major criticism was that this report didn't bother to cite conflicting evidence. It reads like ALL researchers have come to this conclusion. But there are several studies that show that use of social media actually has some positive outcomes for teens, including increased access to social support.